1. Field of the Invention
The present invention relates generally to rotors and electrical machines using rotors, and, more particularly, but not by way of limitation, to permanent-magnet (PM) rotors, rotor components, and machines comprising PM rotors.
2. Description of Related Art
Rotors and machines using rotors have been known in the art for some time. For example, electrical machines such as motors traditionally include brushes and a rotor with wire windings. Such traditional winding-based rotors are relatively inefficient compared with PM rotors, and PM rotors may generally be made smaller than traditional winding-based rotors for a given capacity or output. As a result, machines using PM rotors may generally be made smaller than those with traditional winding-based rotors. PM rotors generally use permanent magnet material instead of traditional electrical wire windings, such that a PM rotor machine does not require reactive current from a power supply. As such, power consumption of PM machines can generally be reduced relative to those using traditional winding-based rotors for a given output. For example, some PM rotor machines can achieve a higher power factor, higher power density, and higher efficiency (e.g., 25% to 120% of the rated load), relative to a traditional winding-based machine. Maintenance costs of PM machines may also be reduced, as the simpler configuration (e.g., without windings, brushes, etc.) may result in fewer parts or points of potential failure.
In some known PM rotor configurations, thin, arcuate PM bulks are mounted to an exterior surface of a rotor core. For example, PM bulks have been glued onto an exterior surface of a rotor core and a non-magnetic ring has been disposed (e.g., glued) around the PM bulks. In this example, there is generally not enough space or insulation between poles (N pole, S pole) of adjacent PM bulks such that flux leakage between poles may be high. This flux leakage may result in relatively poor performance. In another example, the outer surface of a rotor core has been grooved and PM bulks have been disposed in grooves with a non-magnetic ring disposed around the PM bulks. In this example, there is generally magnetic material between the poles (N and S poles) of adjacent PM bulks, often resulting in high flux leakage. Additionally, in this configuration, the d- and q-axis inductances are not symmetrical and complex control configuration is generally needed. In a third example, PM bulks have been attached to the outer surface of a rotor core with radially oriented screws extending through at least a portion of the PM bulks and into the rotor core. In this third example, especially for large or high-speed machines, the centrifugal force in the screws may be enough to loosen the radially oriented screws and undermine the structural integrity of the rotor.